In the drilling of bore holes into or through earth formation, such as, for example, in the drilling of oil or gas wells utilizing a rotary drill bit, it may occur, from time to time, that the bit may be stuck in the earth formation or debris in the bore hole, for example, either due to the caving in of the bore hole wall, or due to the formation of a key seat in the hard earth formation. When the bit is stuck, under such circumstances, it is difficult, if not impossible, to pull the drill string and bit from the bore hole. In the case that the bit is stuck, moreover, the circulation of drilling fluid downwardly through ports usually provided in the drill bit may be impeded or prevented, or may be undesirable.
The circulation of drilling fluid down the running pipe string or the drill pipe string may be impeded because of the caving in of the bore hole wall forming a blockage to the upward flow of fluid from the bit through the bore hole annulus. In the case of in-hole motors, when the stuck bit stalls the motor, the flow of drilling fluid is impeded by the resistance to flow through the in-hole motor assembly. This is particularly true in the case of in-hole motors of the positive displacement type. In addition, if fluid circulation is forced through the stalled motor, the stator of the motor may be damaged or, for example, the elastomeric material of a progressive cavity motor or the turbine elements of a turbine may be washed out by the erosive action of the drilling fluid.
If circulation is interrupted for any significant period of time, the cuttings which are entrained in the drilling fluid in the annulus tend to settle out at the bottom of the bore hole, further aggravating the stuck bit problem.
It is desirable when a bit becomes stuck in a well bore against retrieval from the well bore, either in the case of the usual rotary drilling procedures or in the drilling procedures utilizing in-hole motor drills, that the running pipe string and bit be rotated, while efforts are made to pull the stuck bit free. However, in the case of the typical in-hole motors, rotation of the running pipe string cannot impart rotation to a stuck bit, since there is no positive drive connection between the motor housing and the bit drive shaft.
Circulation valves are known, as shown in Tschirky and Crase U.S. Pat. No. 3,989,114 and in Emery application, Ser. No. 06/047,296, filed June 11, 1979 now U.S. Pat. No. 4,298,077. Such valves have the advantage that the fluid can be circulated througn the open valve, upwardly in the bore hole annulus, to flush cuttings or build up filter cake on the earth formation without necessitating that the fluid pass through the in-hole motor. This saves pump horsepower and wear and tear on the motor and bearings.